1. Field of the Invention
The present invention relates to a capacitive electromechanical transducer that receives an elastic wave such as an ultrasound.
2. Description of the Related Art
A Capacitive-Micromachined-Ultrasonic-Transducer (CMUT) that is of a capacitive ultrasonic transducer is proposed as a transducer that receives an ultrasound. CMUT is prepared using a MEMS (Micro-Electro-Mechanical Systems) to which a semiconductor process is applied. FIG. 8B is a top plan view illustrating a two-dimensional-array CMUT of the related art, and FIG. 8A is a sectional view taken on a line X-X′ of FIG. 8B. In FIGS. 8A and 8B, reference numerals 101, 102, 103, 104, 105, 106, 107, 111, and 112 show a diaphragm, a first electrode (upper electrode), a diaphragm support, an air gap, a second electrode (lower electrode), a first substrate, a through line, an electric connection portion, and a second substrate, respectively (see U.S. Pat. No. 6,430,107).
In the CMUT, the first electrode 102 is formed on the diaphragm 101, and the diaphragm 101 is supported by the diaphragm support 103 formed on the first substrate 106. The first electrode 102, which is formed on the diaphragm 101, and the second electrode 105, which is opposite the first electrode 102 with the air gap 104 (usually, thickness of tens nanometers to hundreds nanometers) interposed therebetween, are disposed on the first substrate 106. Hereinafter, in the first substrate 106, a surface in which the CMUT is formed is referred to as a CMUT formation surface, and a surface on the opposite side is referred to as a CMUT non-formation surface. FIGS. 8A and 8B illustrate a state in which the diaphragm 101 is slightly yielded onto a side of the substrate 106 by an external force. A set of the diaphragm 101, the air gap 104, and the two electrodes 102 and 105 that are opposite each other with the air gap 104 interposed therebetween is called a cell. Plural cells (usually, 100 to 3000 cells) to which the first and the second electrodes 102 and 105 are connected is called an element as a unit in which the ultrasound is transmitted and received. The first substrate 106 includes the plural through lines 107, and lines of the first or second electrodes on the CMUT formation surface are drawn to the CMUT non-formation surface through the through lines 107. The drawn lines are connected to the second substrate 112 through the electric connection portion 111. The second substrate 112 is a Printed-Circuit-Board (PCB) including a multi-layer line or a signal processing chip. In the second substrate 112, elements of the two-dimensionally arrayed CMUTs are connected to a detection circuit or a power supply.